1. Field of the Invention
The present invention relates to a compact speaker for a portable phone, and more particularly, to a compact speaker for a portable phone which enables assembly of a diaphragm and a protector into a frame to be easily achieved without a bonding procedure, so that assembly productivity of a speaker can be improved, and resonant frequency of the speaker can be extremely lowered, thereby contributing to stabilization of sound pressure.
2. Description of the Prior Art
In general, speakers, which are incorporated in a variety of mobile communication equipments such as portable phones (a cellular phone or a PCS (PHS) phone) to generate a ring tone, have been made compact in accordance with the trend toward miniaturization.
Such a speaker is intended to convert electrical energy to kinetic energy by a voice coil positioned in a space on the basis of Fleming's left hand rule, stating that if a conductor through which an electric current flows is positioned perpendicular to the direction of a magnetic field, then that conductor will experience a mechanical force. That is, if a current signal including various frequencies is applied to a voice coil, the voice coil generates kinetic energy depending on levels of a current and a frequency and vibrates a diaphragm attached thereto, thereby generating sound of frequency perceptible to human ears.
Among instruments for generating sound pressure, those which are adapted to generate sound pressure having relatively low intensity and used in close contact with an ear of a human body are referred to as receivers, while those which are adapted to generate sound pressure having relatively high intensity and used at a distance from an ear of a human body are referred to as speakers.
Speakers have a magnetic circuit which is designed to cause magnetic flux from a permanent magnet to be directed perpendicular to a voice coil received in a space by disposing the magnet and a top plate in a yoke of ferromagnetic metal. The voice coil is attached to a diaphragm so that it can generate up-and-down vibration in response to an input signal to vibrate the diaphragm attached to a frame, thereby enabling sound pressure to be generated. Such a diaphragm usually has variously shaped waves thereon so as to achieve excellent response and negation of buckling phenomenon during its up-and-down vibration. In this way, a shape of a diaphragm serves as a design variable having the greatest effect on frequency characteristic.
Although speakers have not undergone major design changes for a long time, they tend to be made continuously more compact, light in weight and high in efficiency in accordance with commercial availability of high energy permanent magnets, development of molding techniques for small components and miniaturization in communications fields.
In particular, miniaturization of mobile communication equipments can be achieved by miniaturization of components having mechanical dynamic characteristics such as receivers, speakers, buzzers and vibrators. For this purpose, research and development is actively carried out to promote the integration of such mechanical components.
Although a major part of common mobile communication equipments such as portable phones have used buzzers up to now in order to generate a ringing tone, speakers having excellent frequency characteristic are gradually substituted for buzzers to meet demand for various kinds of ringing tones suiting users' tastes, preferences or comfort.
A conventional small sized speaker is usually mounted at a certain position of a portable phone as a separate component. Lately, a speaker tends to be integrated to a vibrating motor.
The above type of speaker integrated to a vibrating motor is illustrated in FIGS. 1 and 2. FIGS. 1 and 2 are an exploded perspective view showing the above type of speaker integrated to a vibrating motor and a cross-sectional view showing the assembled speaker, respectively. As shown in the drawings, the speaker 1 comprises a protector 2 formed with a sound holes 2a for allowing a plurality of different sounds to be emitted therethrough, a diaphragm 5 for generating sounds by its vibration due to sound pressure, a voice coil 6 attached to a bottom surface of the diaphragm 5 and adapted to vibrate by voice current applied thereto, and a frame 1 adapted to receive the voice coil 6 and the diaphragm 5 and to allow the protector 2 to be seated therein.
The frame 1 has an annular stepped portion 1a to allow the peripheral rim of the diaphragm 5 to be seated thereon, and an inner surface 1b for receiving the diaphragm 5 and the protector 2.
The protector 2 has a rim 2b, which is adapted to be forcedly fitted to the inner surface 1b and to be in close contact with the inner surface 1b. 
In an assembling procedure of the above conventional speaker, a predetermined quantity of adhesive is applied to an adhesive-applying area “A” of the annular stepped portion 1a on which the peripheral rim of the diaphragm 5 is to be seated, and then the peripheral rim of the diaphragm 5 which has the voice coil 6 attached thereto is bonded to the annular stepped portion 1a with the adhesive therebetween. After completion of the bonding procedure, the protector 2 is forcedly fitted to the inner surface 1b of the frame 1, thereby completing the assembling procedure of the speaker.
However, in the conventional process for bonding a diaphragm to a frame of a small sized speaker by applying adhesive therebetween, an operation for precisely bonding a diaphragm to a frame having a diameter of only about 10 mm is very difficult. Furthermore, when carrying out an operation for assembling a protector into the frame, the protector tends to stick to the frame because of the adhesive applied to the frame.
In addition, the conventional small sized speaker which is assembled by using a bonding technique has disadvantages in that a targeted applying position and the quantity of adhesive can have a great effect on sound characteristics of the speaker.
That is, owing to the effect of adhesive, a minimum resonant frequency of sound pressure generated from a speaker becomes a high level of about 800-1100 Hz, and sound pressure at high frequency is not uniform. Hence, the above-mentioned process has a disadvantage in that it is difficult to apply to actual products (see FIG. 9).
Furthermore, the above conventional process of bonding a diaphragm by means of adhesive has another disadvantage in that productivity of small sized speakers is lowered because an application operation of adhesive must be carefully carried out.